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How to calculate the effective discount on BOGO

How to calculate the effective discount on BOGO. Use the relevant ShopWithShery calculator to verify the math with your own prices, quantities and terms.

Updated August 9, 2026 · Source-backed where consumer guidance is referenced
Short answer

For two equal-price items and no restrictions, buy one get one free is equivalent to 50% off the pair. If the free item must be the cheaper item, the effective discount can be lower.

The calculation to use

Effective discount = free-item value ÷ regular value of all items

Watch for: Do not compare package prices directly when the sizes, quantities, fees or timing of rewards differ.

A practical way to compare the offers

  1. Write down the price, quantity, package size and promotion exactly as shown.
  2. Convert both choices to the same comparison basis: per unit, delivered cost, effective discount or cost per use.
  3. Separate immediate checkout savings from later rewards such as cashback or store credit.
  4. Consider waste, required purchase quantity, recurring commitments and return restrictions.
  5. Choose the offer that fits both the math and the quantity you will realistically use.

Why shoppers get this wrong

Retail offers often present several numbers at once: package size, headline discount, multibuy quantity, loyalty reward and shipping threshold. Human comparison becomes difficult when those numbers use different denominators. Normalizing the offers removes much of that noise.

Use the calculator

Calculate the real effect of discount. See both the final price and the effective savings instead of relying on the headline offer.

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Continue the shopping decision

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